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Thread: Testing high FC levels during Algae treatment

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    cood60's Avatar
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    Testing high FC levels during Algae treatment

    Hi all, here the details of my latest algae fight:

    Have been keeping pool balanced all year
    FC between 3.5-4.5
    Ph stable at 7.5
    TA stable at 50
    CYA had dropped to 30 ish due to lots of rain, evaporation and consequent replenishing with city water
    Last week was very hot ie upper 90 s all week
    I added Liquid CYA to bring CYA to 60 This was no more than two days before the algae showed up

    Yesterday, I brought FC to 12 (forgot to lower Ph first) Also added some cellulose fiber aid to help clearing process, pressure never did rise!

    Did OCLT last night, went from 12 dwn to 9 overnight (it did rain a little during the night)

    I added 9 more gallons of bleach this morning to get to algae shock level of 36…brushed again, Re-checked FC after 3 hours, and the test is not behaving right.
    When I added the powder to the vile, it only turned a light shade of red but I continued by adding drops and as I did, the water turned dark red. After 64 drops, the water turned to a slightly yellowish tint but would never get clear even after adding 15 more drops.
    Ph is off the chart now, TA is 60, not sure what the FC is due to discolored water instead of clear
    Lowered Ph to 7.2, then added 3 gallons of bleach to get to shock level, brushed again. Water is much more clear already but I am concerned about this light yellowish tint to the water in the vial at the end of the drop count. (FYI, the water is clear in the vial when beginning the FC test

    Anyone know what this light yellowish tint might be? And do you think the FC test is valid at the point the red is gone, just not clear water

    Thanks

    Cush Dobbs
    22'x40' IG, Freeform, 26K gal, Vinyl liner pool(2011), three returns plus two step jets, one slide, two skimmers, two LED lights, Stamped Concrete with Aqua PL-Plus Automation panel, Pentair Intelliflo VS, Hayward Pro Series High Rate Sand Filter 500lb, Hayward Turbo Cell T-Cell 15 (SWG) Smart Pool Scrubber60 Robotic Pool Vac.

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    Richard320's Avatar
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    Re: Testing high FC levels during Algae treatment

    It sounds like the FC is too high for the amount of powder. Try it again with two scoops. If you can see undissolved crystals before you try the drops, you have enough powder. Don't even bother testing pH when FC is above 10. The reagent reacts with the high FC and reads artificially high. If you try to lower it, you'll go way too low.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    cood60's Avatar
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    Unhappy Re: Testing high FC levels during Algae treatment

    oops, I did lower it to 7.3 or at least that is what the reading is.

    FC now reads 46 after using two scoops....but the transition to "clear" is still yellowish

    The OCLT directions say the standard is no more than 1 PPM change over night. But at high levels, when shocking (in my case around 40 PPM would the standard change?
    Example: If I do the first OCLT with an FC of 4, and it is 3 in the morning, that is 25% reduction in FC
    If I do an OCLT with 40 PPM and the morning test is 37, that is appx 8% reduction.????


    I also noticed that my CH is 700. That was unusual. I think the city has done something to their water supply. I checked the city water today and it has a CH of just over 600!
    What to do with fill water that comes at 700?
    22'x40' IG, Freeform, 26K gal, Vinyl liner pool(2011), three returns plus two step jets, one slide, two skimmers, two LED lights, Stamped Concrete with Aqua PL-Plus Automation panel, Pentair Intelliflo VS, Hayward Pro Series High Rate Sand Filter 500lb, Hayward Turbo Cell T-Cell 15 (SWG) Smart Pool Scrubber60 Robotic Pool Vac.

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    JasonLion's Avatar
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    Re: Testing high FC levels during Algae treatment

    Performing the FAS-DPD chlorine test when FC is high is a bit more difficult. If you have properly mastered the techniques required for using the test, then the overnight loss limit is still 1.0, as the test is very repeatable even at high FC levels. One of the keys to testing high FC levels is to move along quickly, adding drops rather rapidly especially near the start. If the test takes to much time the result can read higher than actual.

    High CH fill water is manageable, up to a point anyway. You can keep PH and TA lower to compensate for the high CH levels. If you have a lot of evaporation, you might want to think about topping off the pool with water run through a water softener.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    cood60's Avatar
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    Re: Testing high FC levels during Algae treatment

    Thanks for the CH refill tip, I was wondering how I can get the fill water with less CH
    It's hard to count so fast as I miss a number when I blink...LOL
    22'x40' IG, Freeform, 26K gal, Vinyl liner pool(2011), three returns plus two step jets, one slide, two skimmers, two LED lights, Stamped Concrete with Aqua PL-Plus Automation panel, Pentair Intelliflo VS, Hayward Pro Series High Rate Sand Filter 500lb, Hayward Turbo Cell T-Cell 15 (SWG) Smart Pool Scrubber60 Robotic Pool Vac.

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